This invention relates to a method for the adsorption of proteins from various fluids. More specifically, it has been found that proteins can be removed from fluids by adsorption onto amorphous or crystalline materials comprising acidic cogels of silica and an inorganic oxide. In particular, aluminosilicates have been found to be very effective in this adsorption process.
Examples of protein-containing fluids for which this method is effective are fruit juices, wines and protein-containing wastewater streams. Proteins are present in the juice pressed from grapes, particularly in white or rose wines which lack sufficient tannins to cause precipitation of those proteins during processing. The soluble proteins are heat labile and can be precipitated by the hot/cold cycling typically experienced during transportation and storage of wine or juice. The result is the formation of haze in the wine or juice.
The stabilization procedure presently employed by most wineries involves treatment of the wine with montmorillonite or bentonite clays. In a typical bentonite fining process, the clays are dispersed in water or wine to preswell the clay, forming a slurry. The slurry is added to the wine, where it adsorbs the proteins and various other components, and removed by settling and/or filtration. Due to small particle size and the swelling properties, the clay neither dewaters nor filters well, which presents numerous processing difficulties and results in wine loss even after additional processing of the bentonite lees. Moreover, the preparation and addition of the bentonite slurry to the wine requires significant expenditures of time, labor, energy and equipment.
Other methods, adsorptive or otherwise, have been proposed but their actual use is insignificant relative to bentonite fining. U.S. Pat. No. 4,027,046 (Bohm et al.) discloses a fining method in which a colloidal solution of silicon dioxide in water is mixed with a modifying aluminum compound and the beverage for protein removal and flocculation. Numerous other fining agents (e.g., tannin, isinglass, egg white) are employed for a variety of reasons not limited to heat stabilization. Protein removal by adsorption onto Chinese gallotannin and tannic acid on supports such as silicon dioxide has been used, as has the physical separation of proteins by ultrafiltration. Typical reasons for industry reliance on bentonite fining over these other methods are cost, effectiveness and the sensory properties of the fined wine.